Method and device for recovering metals by means of pulsating cathode currents also in combination with anodic coproduction processes

Abstract

The invention aims to achieve effective recovery of metals from process solutions and effluents by means of pulsating cathode currents, preferably with coupled anodic processes. To precipitate metals by means of direct current in electrolysis cells which are undivided or are divided by separators, the pulsating cathode currents are generated by the anodes being divided into stationary strips past which the undivided cathode surface is guided. The current pulses formed on the cathode surface as a result can be varied in form and frequency by the arrangement of the anode strips and by current diaphragms. An apparatus with rotating cylinder cathodes and concentrically arranged anode pockets, the side walls of which function as current diaphragms and flow breakers, is preferred. Not only does the invention allow efficient recovery of metals, but also it allows coupling to various anode processes, e.g. for regeneration of peroxide sulfates and for breaking down inorganic or organic pollutants by oxidation.

1 . A method for recovering metals from process solutions and effluents by means of pulsating cathode currents, also in combination with anodic coproduction processes, by electrolysis by means of direct current in an electrolysis cell which is equipped with cathodes and anodes and is undivided or divided by separators, characterized in that the pulsating cathode currents are generated by the anodes being divided into strips with a width of 2 to 100 mm and, individually or combined in groups, being arranged in a stationary position parallel or concentrically to the cathode surface, while the undivided cathode surface is guided past at a rate of 1 to 10 m/s in a direction perpendicular to the longitudinal extent of the anode strips, the distance between the side walls of two adjacent individual anode strips or the groups of anode strips amounting to at least 1.5 times the perpendicular distance between the center of the anode strips or the group of anode strips and the cathode.  
     
     
         2 . The method as claimed in  claim 1 , characterized in that considerably greater distances are set between some anode strips or some groups of anode strips than between the others.  
     
     
         3 . The method as claimed in claims  1  and  2 , characterized in that internals used as current diaphragms and/or flow breakers are arranged in the spaces between the anode strips or the groups of anode strips.  
     
     
         4 . An apparatus for carrying out the method as claimed in  claims 1  to  3 , comprising: 
 an electrolyte vessel  1 ,  
 at least one rotating cylinder cathode  5  arranged in the electrolyte vessel,  
 at least one drive  4  which is arranged outside the vessel and the shaft of which is directly connected to the cylinder cathode  5 ,  
 one or more sliding contacts  21  for transmitting the electrolysis current to the rotating cylinder cathode,  
 anodes  6  arranged concentrically around the cylinder cathode,  
 in the case of divided cells, in addition separators  13  arranged between the anodes and the cylinder cathode,  
 characterized in that the anodes are formed from perpendicularly arranged anode strips  6  with a width of 2 to 100 mm, which are arranged in anode pockets  8 ,  11  individually or combined in groups, the distance between the individual anode pockets amounting to at least 1.5 times the perpendicular distance between the anode strips and the cathode and their side walls extending over at least 25% of the perpendicular distance between anode strips and cathode and simultaneously serving as potential-shielding current diaphragms and turbulence-increasing flow breakers.  
 
     
     
         5 . The apparatus as claimed in  claim 4 , characterized in that the anode pockets  8 , in the case of divided cells, are equipped with separators  13  and separate feeds and discharges for the anolyte  16 ,  18 .  
     
     
         6 . The apparatus as claimed in claims  4  and  5 , characterized in that the anode pockets  8 ,  11  are distributed unevenly around the cylinder cathode  5 , so that the distances between individual anode pockets amount to a multiple of the distances between the other anode pockets.  
     
     
         7 . The apparatus as claimed in  claims 4  to  6 , characterized in that the drive  4  of the cylinder cathode  5  is arranged inside the electrolyte vessel  1  in a space which is separated off in a liquid-tight and gas-tight manner.  
     
     
         8 . The apparatus as claimed in  claims 4  to  7 , characterized in that a cooler  12  is arranged inside the electrolyte vessel  1 .  
     
     
         9 . The apparatus as claimed in  claims 4  to  8 , characterized in that the rotational speed of the cylinder cathode  5  can be varied by using a frequency-controlled drive  4 .  
     
     
         10 . The apparatus as claimed in  claims 4  to  8 , characterized in that the cylinder cathode  5  consists of special steel.  
     
     
         11 . The apparatus as claimed in  claims 4  to  10 , characterized in that the cylinder cathode  5  is of slightly conical design.  
     
     
         12 . The apparatus as claimed in  claims 4  to  11 , characterized in that the anode strips  9  consist of one of the valve metals titanium, niobium, tantalum or zirconium coated with platinum, with precious metal oxides or with doped diamond.  
     
     
         13 . The apparatus as claimed in  claims 4  to  12 , characterized by the use of ion exchange membranes or microporous plastic films as separators  13 .  
     
     
         14 . The apparatus as claimed in  claims 4  to  13 , characterized in that in the case of divided cells a plurality of the anode pockets  11  equipped with separators  13  are hydrodynamically connected in series.  
     
     
         15 . The apparatus as claimed in  claims 4  to  14 , characterized in that the electrode spacing is kept constant, in the case of a conical cylinder cathode  5 , by the fact that the anodes or anode pockets are arranged in the electrolyte vessel with an inclination which is matched to the cone of the cylinder cathode.  
     
     
         16 . The use of the method and of the apparatus as claimed in  claims 1  to  15  for metal recovery by means of pulsating cathode currents using divided or undivided electrolysis cells, characterized in that at the cathode 
 one or more metals from the group consisting of: copper, nickel, iron, cobalt, zinc, cadmium, chromium, lead, tin, rhenium, silver, gold, platinum and other precious metals are precipitated in compact form and recovered at mean cathode current densities of 2 to 10 A/dm 2  in batch or continuous operation with a depletion level down to as little as 10 mg/l,  
 oxidizing agents peroxosulfate or hydrogen peroxide which are additionally present are cathodically reduced,  
 metal compounds with a relatively high valency which are additionally present are converted into metal compounds with a lower valency of the metals,  
 oxygen being formed at the anodes and/or  
 oxidizing and pickling agents being generated or regenerated,  
 inorganic and/or organic pollutants being completely or partially broken down by oxidation.  
 
     
     
         17 . The use as claimed in  claim 16 , characterized in that, from the exhausted peroxodisulfate pickling solutions, first of all the dissolved metals are completely or partially precipitated cathodically, and at the same time unconverted peroxosulfates are reduced, then the used peroxodisulfates are completely or partially anodically reoxidized at anodes coated with platinum or doped diamond and at current densities in the range from 20 to 100 A/dm 2  and current concentrations of from 50 to 500 A/l, and the pickling solutions which have been regenerated in this way are fed back to the pickling bath.  
     
     
         18 . The use as claimed in claims  16  and  17 , characterized in that in the cathodically treated pickling solution the sulfate concentration as the sum of the metal sulfate and sulfuric acid concentration is 2 to 5 mol/l, the sulfates used being those of sodium, magnesium, zinc, nickel and iron, in each case alone or in the form of mixtures.  
     
     
         19 . The use as claimed in  claim 16 , characterized in that the pollutants broken down by oxidation are cyanides and cyano compounds, organic complexing agents, sulfides, thiosulfates, sulfites, organochlorine compounds, nitrites and amines.  
     
     
         20 . The use as claimed in  claim 16 , characterized in that in the case of divided electrolysis cells the anode and cathode spaces are fed with different process solutions, and the mass transfer through the cation/anion exchange membranes is deliberately utilized to increase and reduce the levels of cations/anions and/or to block the transfer of anions/cations into the other electrode space in each case.  
     
     
         21 . The use as claimed in claims  16  and  20 , characterized in that a process solution which contains metal chlorides is electrolyzed in the cathode space of an electrolysis cell divided by means of cation exchange membranes, while the anode spaces are fed with sulfuric acid or another chloride-free solution.